Fuel systems including fuel tanks may be used to store and provide fuel to engines. For example, a vehicle including an internal combustion engine may include a fuel tank that stores liquid fuels such as gasoline, diesel, methanol, ethanol, and/or other fuels.
Liquid fuels in a fuel tank may evaporate into fuel vapors in the tanks. As such, various fuel vapor management systems may be included in a fuel system. Such fuel systems may be substantially sealed from the atmosphere but may include components configured to vent the fuel system to the atmosphere during certain conditions. For example, a fuel system may include a vapor purge canister for filtering fuel vapors during venting.
If there are leaks in the fuel system, e.g., if there are leaks in the fuel tank, canister or any other component of the vapor handling system, then fuel vapor may escape to the atmosphere contributing to vehicle emissions, for example. Various approaches to diagnosing leaks in vehicle fuel systems are known. In one approach, leak testing is achieved by utilizing a vehicle engine to create a vacuum within the fuel tank and measuring pressure changes over a time period.
In some approaches, engine off natural vacuum (EONV) may be employed for leak testing in a hybrid vehicle system. For example, a normally open canister vent may be closed and a decrease in vacuum may be measured over a long period of time. Such approaches may use correlations between temperature and vacuum build. However, the inventors herein have recognized a number of issues with such EONV approaches. For example, additional hardware and software may increase costs, and long test times in may reduce the feasibility of carrying out a leak test. Additionally, such EONV approaches may degrade during hot ambient temperature conditions. Further, such EONV approaches may not be sufficiently accurate for leak testing, e.g., due to unreliable correlations between temperature and vacuum build (e.g., due to mass transfer between the liquid and vapor in a fuel tank).
In one example approach, an external electric vacuum pump may be used to create a vacuum to perform a leak test in a hybrid vehicle system. However, the inventors herein have recognized that such an approach may increase material and installation costs associated with the installation of such an external electric vacuum pump and associated hardware and software. Further, such active pumps can be costly, noisy, and consume electric power which drains the battery and may result in a fuel economy penalty.
In order to at least partially address these issues, a method for operating a vehicle with an engine comprises: during vehicle motion, passing air through a venturi coupled to the vehicle to generate vacuum; storing the generated in an accumulator; and, in response to a condition, discharging the stored vacuum to a vacuum consuming system of the vehicle. For example, the condition may be an engine-off event, a key-off event, or a refuel event request and the vacuum consuming system may be a fuel system of the vehicle or a fuel evaporative system of the vehicle.
In this way, a passive device that generates vacuum from vehicle motion may be used to provide vacuum to vacuum-consuming vehicle systems. Specifically, by storing the passively generated vacuum, and coordinating the transfer of the stored vacuum to vehicle systems with vehicle operating conditions, it is possible to meet diagnostic and operating requirements even though vacuum is not able to be generated under all vehicle operating conditions. In this approach, costs and noise associated with an active pump may be reduced and, since no power is used to run the passive venturi, vehicle fuel economy may be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.